The bad news, I looked at HID and LED options and there are clearance problems on my early CAV mono to the back of the fender liner. And with HID it would also require a rewire kit with ballast.
The good news, I replaced the halogen bulb that was in the car for 15 years and noticed the output significantly better. Apparently the bulbs age over time and as my wife reminds me regularly, "many things dim with age...".
When the technology develops a bit more and the cooling assembly gets a bit smaller, I'll probably go to LEDs for the simplicity.
While not a big change, here's the car with one side sporting the fresh halogen and the other the old one.